In air conditioning systems, and, in particular, air conditioning systems that can be employed in the automotive area, numerous designs for air conditioning, and, in particular, HVAC units, have been employed. There are many designs, some using plenums or internal dividing walls within the HVAC units, some without use of such plenums. Such water separator plenums in the prior art normally employ smooth walls and rely on the directional changes in the air flow path to remove water content. However, HVAC units with wet plenum designs have often had the difficulty of not being able to efficiently or effectively, remove water from the air, and, particularly, from fresh air, that is introduced into the unit, due to entrainment prior to the outtake of the air from the unit.